Photovoltaic cells, commonly referred to as solar cells, are well known semiconductor devices that convert photons into electrical energy. FIG. 1 provides a cross-sectional view of a conventional solar cell 100 that includes a substrate 101 of a first conductivity type, the substrate frequently comprised of silicon, and a layer 103 of a second conductivity type formed on the substrate, commonly referred to as the emitter, thereby forming a p-n junction at the interface. Solar cell 100 also includes a rear surface electrode 105 that is in contact with at least a portion of substrate 101, and a front surface electrode 107 that is in contact with at least a portion of layer 103. When light falls on solar cell 100, electron-hole pairs are created, which are converted by the solar cell into electrical energy.
To enhance the performance of a conventional solar cell, typically a dielectric layer 109 is deposited on the front surface of the solar cell. Dielectric layer 109 serves dual purposes. First, it acts as an anti-reflection (AR) coating, thereby increasing the percentage of incident light that passes into cell 100, resulting in improved conversion efficiency. Second, it forms a passivation layer on the surface of layer 103. In some solar cells, dielectric layer 109 is comprised of a pair of layers; an inner passivation layer and an outer AR layer.
Solar cells are becoming commonplace in a wide range of applications, both due to the increase in energy costs and the growing environmental concerns associated with traditional energy sources. The switch to solar energy has been aided by the gradually improving performance of solar cells and the steady decrease in cell cost. In a typical application, for example a solar array for use on a residential or commercial roof-top or in a solar farm, a large number of solar panels are electrically connected together, each solar panel comprised of a large array of solar cells.
When a solar panel or an array of solar panels is put into operation, a high voltage in excess of 100V may exist between the panel frame or external grounding and one or more terminals of the individual devices. As a result, an electric field is generated that may create a charge on the dielectric layer or layers used in the fabrication of the cell, for example, passivation and AR layer 109 of FIG. 1. Over time, the accumulation of charge on the dielectric layer(s) leads to surface polarization, which, in turn, induces an electric field on the cell's p-n junction. As a result, shunt resistance and p-n junction characteristics are significantly degraded, leading to a major reduction in cell conversion efficiency and potentially complete cessation of cell power output. Accordingly, what is needed is a solar cell design that is resistant to surface polarization but does not significantly affect the fabrication process, the overall cell manufacturing cost, or the cell's performance. The present invention provides such a design.